The present invention relates generally to attenuator circuits and more specifically to high power precision step attenuator circuits.
High power step attenuators are used in various applications and are particularly difficult to design and build efficiently. For example, one application which uses such attenuators are traffic alert and collision avoidance systems (TCAS) which are used on aircraft. In TCAS systems the attenuators are known as Whisper/Shout attenuators.
These Whisper/Shout attenuators are required to attenuate a transmitted signal in excess of 1 kilowatt peak power, monotonically from 0 dB to 27 dB in 1.+-.0.5 dB increments. The attenuator must meet these specifications over a temperature range of -55 degrees Celsius to +70 degrees Celsius and at altitudes up to 55,000 feet.
Present whisper/shout attenuators require the removal and installation of test select components by a trained technician to achieve the required step accuracy. This calibration process is performed at the subassembly level and may be repeated multiple times to meet the specification requirements over temperature. This is not only a time consuming and costly operation, but reliability can be impacted by the unsoldering and soldering of the test select components. Also, this method does not permit dynamic control of calibration such as for temperature changes.
TCAS and other systems which use high power step attenuators would be improved and costs reduced by a design which eliminates the need to remove and install test select components in order to meet specifications.
Clearly there exists the need for an improved high power step attenuation design.